
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>延时加载</title>
<style type="text/css">
body,div,ul,li{margin:0;padding:0;}
#box{width:770px;margin:0 auto;padding:10px 0 0 10px;background:#f00;overflow:hidden;zoom:1;}
#box li{float:left;width:375px;height:225px;color:#fff;padding:10px 0;display:inline;text-align:center;margin:0 10px 10px 0;background:#000 url(img/loading.gif) 50% 50% no-repeat;}
#box li img.loaded{width:353px;height:225px;vertical-align:middle;}
</style>
</head>
<script type="text/javascript">
var fgm = {
	on: function(element, type, handler) {
		return element.addEventListener ? element.addEventListener(type, handler, false) : element.attachEvent("on" + type, handler)
	},
	bind: function(object, handler) {
		return function() {
			return handler.apply(object, arguments)	
		}
	},
	pageX: function(element) {
		return element.offsetLeft + (element.offsetParent ? arguments.callee(element.offsetParent) : 0)
	},
	pageY: function(element) {
		return element.offsetTop + (element.offsetParent ? arguments.callee(element.offsetParent) : 0)	
	},
	hasClass: function(element, className) {
		return new RegExp("(^|\\s)" + className + "(\\s|$)").test(element.className)
	},
	attr: function(element, attr, value) {
		if(arguments.length == 2) {
			return element.attributes[attr] ? element.attributes[attr].nodeValue : undefined
		}
		else if(arguments.length == 3) {
			element.setAttribute(attr, value)
		}
	}
};
//延时加载
function LazyLoad(obj) {
	this.lazy = typeof obj === "string" ? document.getElementById(obj) : obj;
	this.aImg = this.lazy.getElementsByTagName("img");
	this.fnLoad = fgm.bind(this, this.load);
	this.load();
	fgm.on(window, "scroll", this.fnLoad);
	fgm.on(window, "resize", this.fnLoad);
}
LazyLoad.prototype = {
	load: function() {
		var iScrollTop = document.documentElement.scrollTop || document.body.scrollTop;
		var iClientHeight = document.documentElement.clientHeight + iScrollTop;
		var i = 0;
		var aParent = [];
		var oParent = null;
		var iTop = 0;
		var iBottom = 0;
		var aNotLoaded = this.loaded(0);
		if(this.loaded(1).length != this.aImg.length) {
			for(i = 0; i < aNotLoaded.length; i++) {
				oParent = aNotLoaded[i].parentElement || aNotLoaded[i].parentNode;
				iTop = fgm.pageY(oParent);
				iBottom = iTop + oParent.offsetHeight;
				if((iTop > iScrollTop && iTop < iClientHeight) || (iBottom > iScrollTop && iBottom < iClientHeight)) {
					aNotLoaded[i].src = fgm.attr(aNotLoaded[i], "data-img") || aNotLoaded[i].src;
					aNotLoaded[i].className = "loaded";
				}
			}
		}
	},
	loaded: function(status) {
		var array = [];
		var i = 0;
		for(i = 0; i < this.aImg.length; i++)
		eval("fgm.hasClass(this.aImg[i], \"loaded\")" + (!!status ? "&&" : "||") + "array.push(this.aImg[i])");
		return array
	}
};
//应用
fgm.on(window, "load", function () {new LazyLoad("box")});
</script>
<body>
<ul id="box">
    <li><img src="img/none.gif" data-img="img/1.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/2.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/3.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/4.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/5.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/6.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/7.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/8.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/9.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/10.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/11.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/12.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/13.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/14.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/15.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/16.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/17.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/18.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/19.jpg" /></li>
    <li><img src="img/none.gif" data-img="img/20.jpg" /></li>

</ul>
</body>
</html>
